Electrical thermostat



May 10, 1938. A. J. KERCHER 2,116,836

ELECTRI CAL THERMOSTAT Filed July 19, 1955 2 Sheets-Sheet l INVENTOR. A/VI/IUI' J. ke/che/f ATTORNEY.

Miry 10, 1938.

A. J. KERCHER ELECTRICAL THERMOSTAT Filed July 19, 1935 2 Sheets-Sheet 2 INVENTOR.

,Jr/fiur J Kara/76W 4347 J5 9 BY p ATTORNEY.

Patented May 10, 1938 UNITED STATES PATENT OFFICE Application July 19,

3 Claim.

This invention relates generally to apparatus for controlling flow of electric current in accordance with the temperature of a fluid or other heated body. It has particular application to electrically heated appliances, such as electric ovens or electric water heaters, where it is desired to interrupt current supply when the temperature of the heated air or water reaches a predetermined value, or where maintenance of a predetermined temperature level is required.

It is an object of the invention to provide an apparatus of the above character which will be simple and reliable in operation, and which will serve to control relatively heavy current loads.

Another object of the invention is to provide an apparatus of the above character whichv will make use of elements having diiferent temperature coefllcients of expansion, which will be so coordinated as to afford ample relative movement for a given temperature change to operate contacting mechanism, but which will not necessitate the use of thermostatic elements of undue length.

Additional objects of the invention will appear from the following description in which the preferred embodiments of the invention have been set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

Fig. 1 is a side elevational view, partly in crosssection, illustrating apparatus incorporating the present invention, the particular form illustrated being combined with elements of an electric water heater.

Fig. 2 is a side elevational detail of certain of the operating parts as shown in Fig. 1, but showing different operating positions.

Fig. 3 is a sectional end view of the apparatus .as shown in Fig. 1, the section being indicated by the line 3-3 of Fig. 1.

Fig. 4 is a cross-sectional detail, taken along the line 4-4 of Fig. 1.

Fig. 5 is a side elevational view, partly in crosssection and showing a modification of the invention suitable for use in conjunction with an electric oven.

Fig. 6 is a cross-sectional detail taken along the line H oi. Fig. 5.

Fig. 'l is a diagrammatic view, illustrating typical electrical circuit connections.

Referring first to Figs. 1 to 4 inclusive, the apparatus illustrated includes a mounting designated generally at ll, which may vary as to detail but which in this instance includes a pair of spaced metal plates II and I2. Since in the 1935, Serial No. 32,183

form shown, the apparatus is intended primarily for use with electric -hot water heaters, the mounting serves to carry a plurality of electrical heating elements l3 of the immersion type, together with a thermostatic operating unit It. The elements l3 can be of the type disclosed and claimed in Patent No. 1,671,592, granted May 29, 1928. Briefly, each element l3 consists of a tubular metal sheath i6, having its opposite sides provided with longitudinal creases H, to provide two passages for accommodating an electrical resistance conductor I8. The electrical resistance conductor in this instance is coiled or convoluted, and is disposed within beads or tubes IQ of suitable refractory insulating material. One end of each of the tubes l6 extends through a member 20, to which the plates I i and I2 are secured, and which becomes a part of the general mounting. The free ends of the tubes iii are sealed by clo- -.sure caps or plates 2|.

ent No. 1,671,592 the creases ll terminate short of the closure 2|, thus afiording a lateral passage-way through which the conductor l8 and its tubular insulation I! may extend.

The thermostatic operating unit It preferably includes a tubular metal case 22, which is formed similar to the sheath It for the heating elements l3. One end of this casing likewise extends through member 20 of the mounting, while the free end is sealed by closure cap 23.

Extending longitudinally within the passages 2|, aiforded within the casing 22, are the rods 25 and 26. These rods are preferably made of a metal or metal alloy having a negligible temperature coefflcient of expansion, as for example invar. On the other hand casing 22 is made of a metal or metal alloy having a substantial temperature coeflicient of expansion, as for example nichrome, copper or bronze. Within the closed end of casing 22, there is a rocker 21, havingv a pivotal mounting 28 to the supporting bracket 29. The adjacent ends of rods 25 and 26 have spherical shaped end portions 3| which are adapted to seat in spherical shaped sockets 32, provided in the arms of the rocker. The other ends of rods 25 and 26 are shown projecting from the casing 22. Where a terminal block 33 may be provided for making electrical connection to the heating elements I3. openings 34 can be provided through which the rods are accommodated.

One of the rods 25 and 26 and in this-instance rod 26, is operativeiy connected to contacting mechanism designated generally at 36. The other rod 25 is engaged by abutment means carried by As disclosed in said Patr together by spring 52.

the moimting ill, and which can be constructed as follows:-

A plunger 51] is aligned with rod 25, and is slidably disposed within a sleeve 35. Sleeve 38 is in turn threaded into a member 59, which extends between the two plates ii and i2 and is secured thereto. One end of the sleeve carries ahand adjustment lever ll, by means of which the sleeve can be turned and advanced or retracted with respect to the mounting. Plunger 37 carries a head 53, which is provided with spherical shaped socket M to accommodate the spherical shaped end portion Mi of rod 25. A compression spring M has its one end seated upon the head 53, and its other end seated upon the adiacent end of sleeve 3&3. The outer end of plunger 3? is provided with some suitable form of limiting shoulder, as for example, it can be threaded to accommodate the lock nuts 45. It is apparent that the abutment means described serves to ap ply force to rod 25 against the rocker 2?, by virtue of the compression spring M. The magnitude of this force and the positioning of sleeve 38, can be varied by changing the setting of lever M.

The contacting mechanism may be a simple set oi electrical contacts adapted to be opened and closed by relative movement between the outer end of rod 25 and the mounting ill. However, for handling relatively heavy current loads, a more elaborate type of contacting mechanism is desirable, in order to avoid arcing. The mechanism illustrated is of the relay type, and includes a magnetic core 5i, one leg of which is provided with the winding 52. Near the poles of the core 5i there is a magnetic armature 53, carried by pivot pin 55. Armature 53 carries a movable contact 55, adapted to cooperate with a stationary contact 517. While various expedients can be utilized for attaching contact 55 to the armature 53, the arrangement illustrated utilizes a block 55 of insulating material, mounted upon the armature 55. "Qverlylng the upper face of block 58, there is a metal strip 59, which carries the contact 56. A. threaded pin 59 is mounted on block 58, and extends loosely through the metal strip 59. A light compression spring 52 presses down upon strip 55, and has its upper end seated upon an adjustable nut 85. Metal strip 59 also carries a depending stud M, which extends loosely into a recess 55 provided in block 58. Thus when armature 55 is pulled downwardly by coil 52, a certain amount of lost motion is provided between the insulating block 58 and the metal strip 59, so that contacts 55 and 571 are resiliently urged A suitable spring Bl can be provided for lifting the armature 55, and thus causing the contacts 55 and 5? to open, when the core 5i is deenergized.

In addition to the armature 53 there is a lever 68, which is carried by a pivot pin 69. Immediately below pivot pin 69 the lever is provided with a spherical shaped socket ii, in which the adjacent end portion '52 oi rod 25 is seated. As viewed in Fig. l, lever 58 is urged to turn in a clockwise direction about the pivot pin. 69, by a leaf spring is. Lever 55 carries a movable electrical contact TM, which is adapted to cooperate with a stationary contact 175. Contacts 5?? and 15 are directly electrically connected with each other, as illustrated.

As representative of suitable arrangement for supporting the contacts M on lever 55, this contact is shown carried by a threaded stud ill, which in turn is adiustably carried by one end of a metal strip 18. Metal strip ill is carried by an insulating block it, which is a part of lever 68.

In order to afiord an interlock between lever 68 and armature 53, the lever carries an upward extending spring tongue iii, the upper end of which is shaped to form a latch 82. Swinging of tongue M in one direction is limited by a relatively rigid portion 83 of the lever 68. Latch 82 is adapted to engage a dog 84, formed upon the free end of armature 55.

Mounted on the lever 68, adjacentthe open leg 85 of core 5!, there is a magnetic armature 55. The adjacent core leg 85 is slotted to accommodate a shading coil 81.

The typical circuit connections shown in Fig. 7, can be briefly explained as follows:0ne side of the current supply line i is shown connected to terminal of the electrical heating unit Ma. The other current supply line 2 is connected to the stationary contacts 5? and 16. One terminal of relay winding 52 is connected to contact [4, and the other to the other terminal of the heating unit I311. The heating units also connect to the movable contact 55, whereby when contacts 55 and 5'! are closed, the heating units are connected directly across the current supply.

Operation of the apparatus described above, can now be explained as follows:Assuming operation with a hot water heater, the heating units 83, as well as the casing 22 of the thermostat operating means, extend into a water tank, or into a chamber through which water to be heated is being circulated. Lever 4| is set in accordance with the temperature at which it is desired to interrupt the flow of current, as for example 180. While the lever 68 is latched with respect to armature 53, the main contacts 55 and 57 are closed, and current is supplied to the electrical heating units. Likewise at such time the relay winding 52 is short circuited, and no current flow occurs through the same. Lever 58 is held in closed position by virtue of the pressure of spring 4?, which is transmitted through rod 25, rocker 2i, and rod 26. As the tempera- 'ture of water surrounding casing 22 increases,

heating of this casing causes it to expand longitudinally, while the rods 25 and 26 do not ex pand. Thus if plunger 31 were fixed, relative movement would occur between the closed end of the casing 22 and the corresponding end of rod 25, to cause rotation of the rocker 2''! in a counter-clockwise direction, as viewed in Fig. 1, and such relative movement would be transmitted to rod 26. However since rod 26 would likewise remain of fixed length, the relative movemerit between the end portion 12 of rod 26 and the mounting iii, would amount to substantially twice the change in length of casing 22, by virtue of thermal expansion. Since plunger 31 is resiliently urged against rod 25 by compression spring 41!, it may initially move somewhat relative to the mounting as the temperature increases, until lock nuts 68 engage the outer end of sleeve 38. Further expansion of casing 22 causes relative movement between the end portion E2 of rod 26 and the pivot pin 69, thereby causing lever 58 to swing towards open position, to open contacts M and I6, and to displace the latch 52 with respect to dog 84. Armature 53 now snaps to open position under the urge of spring 5?, to open the main contacts 56 and 51, and to interrupt supply of current to the heating units. Full open positions of the levers 68 and 55, are shown in Fig. 2. When the casing 22 has cooled at sumcient amount, its contraction causes lever 68 to swing in a counter-clockwise direction, as shown in Fig. 2. Such movement serves to close the contacts 14 and 16, which as will be evident from the circuit diagram of Fig. 7, connects the relay winding 52 across the current supply lines I and 2, in series with the heating units i3a. Magnetization of core 5| immediately causes armature 53 to snap to closed position, which again causes the latch 82 to engage the dog 84. For the short interval that core 5| is energized, the magnetic pull of core leg 85 upon armature 8G, prevents vibrating movements of lever 58, and thus chattering of contacts 14 and 16 is prevented.

It is a simple matter to adjust the apparatus for diiierent temperature level of operation, by changing the setting of lever 4|. It will be noted that the type of abutment means utilized in conjunction with this lever, for pressing upon rods 25, avoids displacement of parts or possible breakage when the casing 22 is relatively cool. The multiplied motion secured by utilizing two rods 25 and 26 in a single expansible casing, makes it possible to avoid the use of casings of undue length, and at the same time makes possible accurate regulation at a desired temperature level. Likewise in the particular type of apparatus illustrated, in which heating units are grouped in close proximity to the casing 22, the water is caused to thermally circulate about the casing 22, and the casing 22 is heated to a temperature somewhat higher than the temperature of the main body of water being heated, so that it will in efiect anticipate a desired temperature level, in interrupting the current supply. Furthermore, if for some reason water should be drained from the heater, the casing 22 will be heated by radiation from the units l3, and by hot currents of air, so that under such conditions it will interrupt the current supply before the heating units are permanently injured by an unduly high temperature.

The modification illustrated in Figs. 5 and 6 is similar to that previously described with reference to Figs. 1 to 4 inclusive, except that it is intended particularly for use with electrical ovens, such as are employed on domestic cooking ranges. In such applications the casing 22a is arranged to extend into the oven compartment, preferably in relatively close proximity with the heating elements. The outer surface of easing 22a is shown provided with'scarf lines or grooves Si, in order to afford a greater exposed area, and

.thercby increase heat transfer with respect to the surrounding air. A modified form of abutment means for engaging the rod 25, is also illustrated, and is constructed as follows:An L 92 is carried by pivot pin 93, and has its one arm provided with a socket 94, in which the end portion 46 of rod 25 is seated. The other arm 96 ()l lever 92 is forked and is connected to one end of a tension spring 91. A rod 98 is threaded into a member 99, which in turn is carried by the two plates II and I2 of the mounting. A collar llll is formed on rod 98, and one face of this collar bears upon the raised portions I02 of arm 96.

It is evident that the type of abutment means described with respect to Figs. 5 and 6, operates in substantially the same manner as the abutment means disclosed in Figs. 1 to 4 inclusive. When the apparatus has been set for operation at elevated temperatures, as for example, between 205 and 500 F., collar lfll will be spaced from the portions I02, when the casing 22a is cold.

I claim:

1. In an electrical thermostat, a mounting, an elongated tubular casing having one end of the same secured to said mounting, the other end of said casing being closed, said casing being formed 0 metal having a substantial temperature coeilicient of expansion, a pair of metal rods extending longitudinally through said casing in parallel relationship, a rocker pivotally mounted in a closed end of said casing and having its arms connected to corresponding ends of said rod, both said rods being made of metal having negligible temperature coemcient of expansion, contacting means actuated by relative movement between the other end of one of the rods and said mounting, and means for adjusting the temperature level of operation of said contacting means, said last means including an adjustable abutment carried by the mounting and engaging that end of the other rod removed from said rocker, said last means including a movable abutment engaging that end of the other rod remote from the rocker, a spring serving to urge said abutment against its associated rod, and adjustable means serving to limit movement of the abutment in one direction.

2. In a thermostatic device, a mounting, an elongated casing having one end of the same secured to said mounting and being formed of material having a substantial temperature co-efllcient of expansion, that end of the casing remote from'said mounting being closed, a rocker pivotally connected to said casing within said closed end, a pair of rods extending longitudinally within said casing, said rods being formed of a material having a negligible temperature coeflicient of expansion, connections between the corresponding ends of said rods and the arms of said rocker, adjustable abutment means for the other end of one of the rods, said abutment means normally serving to limit the longitudinal movement of saidone rod in a direction towards said mounting, but permitting movement in an opposite direction, a spring associated with the abutment means and against which the abutment means may yield when said one rod is moved relative to the mounting beyond said limit, and response means actuated by relative movement between the mounting and the other end of the second rod, said last means including a movable member engaging the second rod, and a second spring for urging said last named member in a direction to urge the second rod towards said rocker, said second spring being incapable of supplying sufllcient force to efiectively overcome the force of the first named spring.

3. In a thermostatic device, a mounting, an elongated casing having one end of the same secured to said mounting and being formed of material having a substantial temperature co-eflicient of expansion, that end of the casing remote from said mounting being closed, a rocker pivotally mounted within said casing at a point remote from said mounting, a pair of rods extending longitudinally within said casing, said rods being formed of a material having a negligible temperature co-efiicient of expansion, connections between the corresponding ends of said rods and the arms of said rocker, adjustable abutment means for the other end of one of the rods, said abutment means normally serving to limit movement of the one rod in a direction toward the mounting but permitting movement in an opposite direction, a spring associated with the abutment means and against which the abutment 4 emeeae means may yield, and response means actuated by relative movement between the mounting and the other end of the second rod, saidlast means including a lever pivotally carried by the meuntmg and capable of limited oscillating movement, one arm of said lever having abutting engagement with the adjacent end of the second met, and a spring serving t0 urge said lever in a directton to force said arm against said second rod, the force thus exerted by said second named spring being normally applied against the force of the first-named spring but being incapable of overcoming the force exerted by the first named spring.

ARTHUR J. KERCHER. 

